1. Technical Field
The present invention relates to a piezoelectric element module, an ultrasonic transducer, a liquid ejecting head, a liquid ejecting apparatus, and a piezoelectric element module manufacturing method.
2. Related Art
Ultrasonic sensors, which are exemplary ultrasonic devices including ultrasonic transducers using piezoelectric elements, include two types, integrated transmitter/receiver ultrasonic sensors and separate transmitter/receiver ultrasonic sensors. Guidelines for selecting a piezoelectric element are that, at the time of transmitting ultrasonic waves, it is important that the amplitude vibration upon application of voltage is large, that is, a piezoelectric constant d33 is large, whereas, at the time of receiving ultrasonic waves, it is desirable that the voltage generated upon application of pressure be large, that is, a piezoelectric voltage constant g33 be large.
Lead zirconate titanate (PZT) having a composition of a morphotropic phase boundary (MPB) at which the piezoelectric constant d33 is large has been used as an element. However, although such a PZT is excellent in terms of transmission performance, there has been a problem in that, since PZT has a large relative dielectric constant, the piezoelectric voltage constant g33 is small and the reception performance is inferior.
To address this problem, for example, an ultrasonic sensor that aims to improve performances by optimizing the arrangement pattern of units in a separate transmitter/receiver structure has been proposed (see JP-A-2010-183437). Another ultrasonic sensor that reduces sound diffraction and residual vibration by providing a gap between units in a separate transmitter/receiver structure has been proposed (see JP-A-2011-82624).
However, the ultrasonic sensors disclosed in JP-A-2010-183437 and JP-A-2011-82624 have not yet attained sufficient sensitivity. Sensors with more satisfactory sensitivity have been desired.
Note that, both in JP-A-2010-183437 and in JP-A-2011-82624, piezoelectric elements of the transmitting unit and the receiving unit are the same, and different piezoelectric elements are not provided to the transmitting unit and the receiving unit probably because it is difficult to manufacture an ultrasonic sensor with such a configuration.